An inter-university team of researchers that includes Assistant Professor Zlatan Aksamija and graduate student Arnab Majee of the Electrical and Computer Engineering Department has published a scientific paper in Nano Letters ("Bimodal Phonon Scattering in Graphene Grain Boundaries") examining how heat transfer works in graphene, the one-atom thick sheets of carbon. The team found that as grains of the material become more misaligned, the heat transferring properties decline. Read related article in Nanowerk News, Chemeurope.com, Nanotechnology Now, and Science Newsline.
According the Nanowerk News, the researchers have solved the long-standing conundrum of how the boundary between grains of graphene affects heat conductivity in thin films of the miracle substance, thus bringing developers a step closer to being able to engineer films at a scale useful for cooling microelectronic devices and hundreds of other nano-tech applications.
As the Nanowerk article explained, “Since its discovery, graphene – a single layer of carbon atoms linked in a chicken-wire pattern – has attracted intense interest for its phenomenal ability to conduct heat and electricity. Virtually every nanotech device could benefit from graphene’s extraordinary ability to dissipate heat and optimize electronic function, says Poya Yasaei, UIC [University of Illinois at Chicago] graduate student in mechanical and industrial engineering and first author on the paper.”
Nanowerk News added that “In a two-year, multidisciplinary investigation the researchers developed a technique to measure heat transfer across a single grain boundary and were surprised to find that it was an order of magnitude – a full 10 times – lower than the theoretically predicted value. “They then devised computer models that can explain the surprising observations from the atomic level to the device level.”
According to the Nano Letters abstract: “Graphene has served as the model 2D system for over a decade, and the effects of grain boundaries (GBs) on its electrical and mechanical properties are very well investigated. However, no direct measurement of the correlation between thermal transport and graphene GBs has been reported. Here, we report a simultaneous comparison of thermal transport in supported single crystalline graphene to thermal transport across an individual graphene GB. Our experiments show that thermal conductance (per unit area) through an isolated GB can be up to an order of magnitude lower than the theoretically anticipated values. Our measurements are supported by Boltzmann transport modeling which uncovers a new bimodal phonon scattering phenomenon initiated by the GB structure. In this novel scattering mechanism, boundary roughness scattering dominates the phonon transport in low-mismatch GBs, while for higher mismatch angles there is an additional resistance caused by the formation of a disordered region at the GB. Nonequilibrium molecular dynamics simulations verify that the amount of disorder in the GB region is the determining factor in impeding thermal transport across GBs.”
Aksamija is part of the Nanoelectronics Theory and Simulation Laboratory, which focuses on theoretical and computational nanosciences with engineering applications related to emerging semiconductor nanostructures, post-CMOS nanoelectronic devices and computing paradigms, and nanoenergy materials.